SDR does not mean direct sampling.
Correct. Direct sampling, superhets, and direct conversion rigs all can be SDRs. If the software is implementing part of the RF physical layer (not just DSP processing the already analog demodulated receive audio), then, according to the IEEE definition, it's an SDR.
Can a boatanchor with IF buffer stage and downconverter to >=16 bit soundcard be considered SDR according to the IEEE definition?
IIRC, one of the first amateur radio SDRs from the mid-90's was a Kenwood model, where the radio's speaker could reproduce sound maybe up to 10 kHz, but the software demodulated samples from an IF of 11 kHz... so it could be called an SDR, instead of an analog radio with an added audio DSP. (Maybe 11 kHz is an IF frequency for old guys, but it's audio for a dog.)
This is still being done. My mcHF QRP SDR transceiver uses an IF of 12 kHz.
Other Tayloe design direct conversion SDR receivers use an IF of 0 Hz, but producing IQ samples, thus allowing software to filter and demodulate "negative" complex IQ frequencies below the 0 Hz baseband, thus working on samples that are not yet completely demodulated in analog hardware.